One shot of Natasha Romanoff/Scarlett Johansson with Y/n

My girlfriend's sister-Natasha Romanoff

It had been a while since you were in a relationship with Yelena. You met her in a cinema and she took a chance to go and talk to you. It instantly clicks between you two and you've never been more in love. You knew all about her of course. Expect one thing. She had a sister. Pretty hot might you had. After 4 years of relationship, not once she mentioned her sister. You met Natasha when one day she called Yelena that she wanted to see her little sister since it's been so long.

Flashback 3 months ago***

You were cooking diner for your girlfriend and yourself when suddenly she burst into the room panicking. You put the stove on low and rush towards her. "What's wrong baby?" "There is something you don't know and I'm scared to tell you." You look at her in the eyes and said. "You know you can tell me anything baby." She smiled at you and respond. "Well, I never told you this because I haven't seen her in such a long time because she went to another country but here you go. I have a sister. Her name is Natasha. I-I don't know why I never told you but I'm sorry I-" You cut her rambling by putting your lips on hers in a small kiss. When you pulled back you smiled at her. "I'm not mad, but why are you telling this to me now?" "Because she will come to visit us." "That's great baby! When?" She looked nervous all over again. "Well hmm, right now?" Your eyes widen and said "What do you mean right-" And you got cut by a knock on the door. She smiled shyly at you and went to open the door. Luckily for you, you had made enough food for another person. You went back to cooking when You heard Yelena and another voice. "Love, this is my sister, Natasha. Nat, this is Y/N" Two minutes ago you could've sworn that Yelena was the most beautiful girl you ever saw, but right now, she was in great competition with her sister. Red hair, big breast, body shaped like an hourglass, perfect. Natasha made her way to you and hold out her hand. "Hi, nice to meet you." You smiled at her and said the same thing. When you shook her hand you felt a spark through your arm. You know she felt it too because she removed her hand immediately and try to act as nothing happened. After that, you all ate diner getting to know each other. Natasha told you that she will stay in town for a while because she had to take a long vacation from work. You hoped that she wouldn't stay long because it might become a problem...

End of flashback***

Here you were, 3 months later, thinking about your feelings for Yelena and Natasha. This is crazy. You can't be in love with both. You only knew Natasha for a couple of months and she already got under your skin. You could see the way she was looking at you and it wasn't helping. You didn't know if it was lust or whatever in her eyes but either way, it was getting to you. Every time she was around you were getting horny and when she was gone you would fuck Yelena like there was no tomorrow. I mean. At least you weren't cheating but you felt bad nonetheless. She always had been amazing with you and here you were thanking her by developing feelings for her sister. Fucking great.

Right now you were alone with Natasha sitting on the couch, watching a movie. Yelena was working and wouldn't be home for the next two hours at least. You had all planned to go to the restaurant but Yelena got called in for work so you had to push the reservation to three hours later. That's why Natasha was sitting beside you, too close for your liking. It was one of the first times that you were alone with her and you couldn't help but be grateful. This way, you didn't have to control your desire for her since Yelena was there. You still loved Yelena deeply and will never cheat on her. But you couldn't help but feel some deep attraction for the redhead next to you. You were so deep into your thought that Natasha had to shake you to bring you back to reality. "Y/N! Are you ok?" "Yeah, I'm fine."  She let it slide and continued to listen to the movie. After a couple of minutes, you told Natasha you wanted popcorn and she did too so you got up and went to the kitchen. You put two bags of popcorn in the microwave and waited. Out of nowhere, Natasha had pinned you on the counter and her face was inches apart from you. Too confused to push her away you stuttered. "W-what are you d-doing." "I tried to stay away from you because you're my sister's girlfriend but I can't anymore. I want you so bad, I know you want me to. I know our feelings are the same. You felt the spark too didn't you?" You looked her in the eyes and said. "Y-yeah I did. It might be true but I'm with Yelena and I'm in love with her." She seemed sad but didn't let go. "Ok but you and I both know we have feelings for each other, why not give it a try?" Now you push her off you. "We can't! Think about Yelena in this? Don't you want her to be happy?" "Yes, I do. But you... I can't stop thinking about you." You let out a shaky breath and said. "Look Nat, you're right, I have developed some feelings for you over the past months, but I can't and I don't want to leave Yelena for this because I'm still in love with her." Natasha had tears in her eyes but nod her head. "Alright, I get it. But I won't go with you tonight, might as well make this a date with Yelena." With that, she took her things and walk to the door. "Nat-" And she was gone. Saying this to her made your heart ache. Was this the best decision for you? You might never know...